Eski Arktik ipuçları, kış deniz buzu kaybının sanılandan büyük olabileceğini gösteriyor

The summer retreat of Arctic sea ice is widely discussed, yet winter ice matters too, since it regulates how much heat and moisture reach the atmosphere, and climate models disagree with one another most about this season. A team from Cambridge and Mexico’s CIMAT, writing in Nature Geoscience, turned to the mid-Holocene, about 6,000 years ago, when small shifts in Earth’s orbit helped make the Arctic warmer. From ocean sediment cores they assembled the largest database so far of IP25, a chemical marker made by sea-ice algae, and used it to estimate past ice cover. They compared these estimates with 27 climate models and, through Bayesian weighting, gave more influence to models that reproduced the past more closely. Applied to recent and future simulations, the weights showed that the models had overestimated winter ice, so future winter cover may be about a million square kilometres smaller than earlier projections, with uncertainty reduced by up to 85 percent.